Calculate the potential difference and resistance...10 points to best answer?

Question

Please look at the diagram below

http://i71.photobucket.com/albums/i159/JogaBonito7/c2.gif

(1) Calculate the total resistance in the circuit

(2) the current, I drawn from the batteries

(3) the potential difference across the 18 ohm resistor

Answer 1

There's effectively a 30 Ohm resistor in Parallel with a 10 Ohm resistor

1. 1/Rt = 1/R1 + 1/R2

1/Rt = 0.13333 Ohms

Rt = 7.5 Ohms

2. I = V/R = 3/7.5 = 0.4A

3. P.d. across top branch = p.d. across bottom branch = 3V

the ratio of p.d. across the 12 and 18 Ohm resitors equals the ratio of resistance between them as V is proportional to R.

P.d. = 18/30 x 3 = 1.8V